In conventional coating hoppers, including those used for supplying photographic emulsions, material flow into the hopper is either center fed or end fed. In both flow patterns, achieving adequate widthwise flow distribution is a problem. To accomplish adequate widthwise flow distribution, contouring of the manifold and lips is often provided. The contouring is needed to offset the pressure loss which occurs between the inlet in the far end of the manifold. Properly done, the method is adequate for a specific set of fluids and flow conditions. However, a change in flow conditions or fluids will typically alter the pressure relationship in the manifold and create unacceptable flow distribution.
Rather than contouring the manifold, a different flow path or flow circuit has been shown to evenly distribute the pressure of the fluid. One such flow circuit is a criss-cross circuit. However, the added complexity of the passages needed in the hopper body requires special methods of hopper construction which include maintaining the mechanical stability of the delivery slot.
Prior art attempts to solve the above problem are disclosed in U.S. Pat. Nos. 4,344,907; 4,552,521; 4,619,802 and 4,789,513. Each of the aforementioned references disclose the use of inserts for a dye for the purpose of combining two or more materials. However, none of these patents teach improvements in total flow uniformity. Other patents, for example U.S. Pat. Nos. 4,017,240; 4,411,614 and 4,826,422 each use some sort of insert to achieve flow uniformity of a single stream. However, the '240 and '614 references do not show appreciation for the specific problem faced by the applicant because they teach branching the flow into various channels which all empty into a final damping cavity. The '422 patent achieves its results by branching the flow into layers that overlap when they recombine in the damping cavity.
Furthermore, U.S. Ser. No. 08/098,179 filed Jul. 28, 1993 teaches the use of inserts to achieve uniform flow in a criss-cross hopper. However, the inserts used in this hopper can affect the gauging of the delivery slot.
Accordingly, the present invention presents an apparatus for achieving uniform flow distribution in a criss-cross hopper while providing a final slot dimension that is very accurate, even after repeated disassembly and reassembly.